SAMPLEClassification and Cavity

Preparation for Caries LesionsG. J. Mount ! W. R. Hume14

A s discussed in other chapters ofthis book, when demineralisa-tion becomes dominant and

remineralisation fails, a carious lesionwill develop on the enamel or the rootsurface of a tooth. Once the lesion hasprogressed into the dentine there is aneed for some level of surgical inter-vention to remove the infected den-tine, to eliminate surface cavitation andavoid further accumulation of plaque.In most situations this will involveremoval of a certain amount of enamelto achieve access but it must be notedthat both enamel and dentine arecapable of being remineralised andtherefore conserved. The principle ofminimal intervention operative den-tistry is based upon maximum preser-vation of natural tooth structure tomaintain the strength and integrity ofthe tooth crown. This Chapter offers anew look at the identification, classifi-cation and treatment of lesions frominitial demineralisation to the treatmentof extensive coronal breakdown.

Up to the present time the professionhas used a classification of cavities pro-posed by G. V. Black over one hundredyears ago. The classification wasdesigned before the widespread use ofradiographs so lesions were not diag-nosed until they were visible to thenaked eye and were therefore, bymodern standards, relatively large.

A further problem was that it was aclassification of cavity designs for amal-gam as this was the principal restorativematerial available. The result was that,regardless of the size of the lesion, aspecific cavity design was required todeal with it. Today current knowledgeoffers many alternatives ranging fromearlier diagnosis of caries activity, alongwith effective methods of control, tothe application of adhesive and bioac-tive restorative materials. If our patientsare to reap the full benefit of theseadvances it is necessary to review boththe classification and the approach tothe surgical treatment of lesions whenthey progress beyond remineralisationalone.

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244 Preservation and Restoration of Tooth Structure

Introduction

Defects on the crown or root surface of a toothcan arise from one or more of the following

four causes:� developmental defects in the enamel surface� bacterial caries� chemically stimulated dissolution or erosion� physical abrasionProbably the most common problem arises from

a combination of bacterial caries beginning inrelation to a developmental defect. This is con-firmed by repeated surveys showing that the mostfrequent lesion requiring treatment is occlusalcaries, primarily in molars but also in bicuspids.The next lesion in terms of frequency is bacterialcaries developing in relation to the contact pointbetween pairs of teeth - both posterior and anteri-or.

In recent years there has been an increasingproblem in relation to chemical erosion of bothenamel and dentine and this can generally betraced to increased intake of acid food and drinkallied to vigorous tooth brushing shortly afterintake. Physical abrasion is generally related toocclusal irregularities but can often also be relat-ed to chemical dissolution at the same time.

All of these problems can lead to sufficient lossof tooth structure to require repair or replacementbut, at the same time, all can be prevented, sta-bilised or healed to some degree. It is importantthat there is a means of properly classifying andidentifying all these lesions at the time of initialexamination so that a proper logical treatmentplan can be formulated to not only repair the dam-age but, more importantly, eliminate the cause.

With this approach in mind this chapter outlinesa proposal to introduce a new classification forlesions of the crown of the tooth and then goes onto offer some suggestions for repairing thelesions. It is important to note that the classifica-tion does not specify a cavity design. These essen-tial details must be left to the informed and soundclinical judgement of the operator whose mainaim at all times should be preservation of as muchnatural tooth structure as possible.

A New Cavity Classification

The reasons for a new classification

The classification used at present by the profes-sion goes under the name of its author, Dr G. V.

Black.1 The centenary for the introduction of thisclassification is well past and there have beenmany changes and much progress in the under-standing of caries, as well as other forms of pro-gressive loss of tooth structure. The inherent limi-tations of the present classification are far too rigidfor simple modification and it is suggested that itis time to get serious about reviewing the concept.

Probably the most significant discovery that hashad a major impact on the practise of operativedentistry is the understanding of the ion migra-tion that occurs, both out of and back into toothstructure, as a result of the caries process. It isnow recognised that this is reversible, so the earlylesion can be healed and recognition of the initia-tion of the disease process is imperative. After all,a cavity (loss of tooth substance) is an advancedsymptom of a bacterial disease (or chemical disso-lution) that has been in progress for some time. Itis also apparent that there is a gradation of miner-al loss from the heart of the lesion outwards to theperiphery of the lesion. This implies that, simplybecause some section of the tooth is partly dem-ineralised, it does not necessarily have to beremoved because remineralisation may still bepossible.

The second significant discovery is the develop-ment of sound long term adhesion betweenrestorative materials and tooth structure. This notonly reduces the potential for microleakagebetween restoration and tooth but also offers thepossibility of reinforcing the tooth crown, at leastto the limit of the tensile strength of the material.

A third innovation is the development of arestorative material that is capable of supportingan ion exchange within the tooth crown. This notonly leads to an ion exchange mechanism foradhesion but also assists the remineralisation ofdemineralised enamel and dentine.These threediscoveries alone significantly undermine theoriginal precepts behind the G. V. Black classifica-

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Classification and Cavity Preparation for Caries Lesions 245

tion and suggest that there should be change. Oneof the greatest advantages of introducing a newclassification is the possibility of recognising allnew lesions from the very earliest stage and treat-ing them in the most conservative minimallyinvasive manner possible.

At the same time it is necessary to accept that allrestorative dentistry up to the time of the intro-duction of change will have been carried outusing Black�s principles. In other words, it isessential to take both concepts into account at thesame time because it is not possible to carry out asimple substitution of one for the other.Breakdown of old restorations needs to be recog-nised separately as �replacement dentistry� andthere is little or nothing that can be done for theseapart from minimising the loss of further toothstructure.

The following apologia to G. V. Black is offeredto assure the reader that the authors understandthe historical significance of a great man and aleader of the profession.

The G. V. Black ConceptWhen Black defined the parameters for his classi-fication, the cavity designs were controlled by anumber of factors many of which no longer apply.Caries was rampant and the role of bacterial floraand the significance of fluoride were not under-stood. Radiographs were not in general use so, onaverage, a cavity was not diagnosed until it waslarge enough to be identified with a sharp probeor seen by the naked eye. By modern standardsthat meant it was well advanced. There were limi-tations in the available instruments for cavitypreparation as well as the selection of restorativematerials. The classification offered a series ofcavity designs related to the site of the lesion butthe list was then modified to suit the intendedrestorative material. Because all cavities, bytoday�s standards, were large he did not take intoaccount the increasing dimensions of a cavity northe varying complexity of the method of restora-tion. Black suggested that it was necessary to

� remove additional tooth structure to gainaccess and visibility

� remove all trace of demineralised enamel

and dentine from the floor, walls and mar-gins of the cavity

� make room for the insertion of the restora-tive material in sufficient bulk to providestrength

� provide mechanical interlocking retentivedesigns

� extend the cavity to self-cleansing areas toavoid recurrent caries

In his designs Black showed commendablerespect for remaining tooth structure as well asocclusal and proximal anatomy but it was neces-sary to sacrifice relatively extensive areas of enam-el and dentine to achieve his goals. Other far moreeffective methods of dealing with a carious lesionare now available. With modern understanding ofadhesion and remineralisation it is no longer nec-essary to remove all unsupported demineralisedenamel around the cavity margin, the concept ofself-cleansing areas has been discarded andremoval of all affected dentine from the axial wallof the cavity is strictly contraindicated because ofthe potential for remineralisation and healing.

Many of the old limitations no longer apply andit is now appropriate to think again about the prob-lems presented by a carious lesion. Without in anyway denigrating the achievements due to Black�sconcepts and work, the following thoughts areoffered and a new approach to the definition ofcavity design is outlined. The proposed classifica-tion is designed for the identification of lesionsfrom the very earliest stage of demineralisationand to define their increasing complexity as thelesion extends. It is expected to provide benefitsfor both the profession and their patients.2-5

Classification of lesions of the exposed tooth surfaceIt is suggested that caries lesions occur in onlythree sites on the crown or root of a tooth, that is,in those areas subject to the accumulation ofplaque. Therefore, the first parameters for theclassification are these sites:

� Site 1 � pits, fissures and enamel defects onocclusal surfaces of posterior teeth or othersmooth surfaces

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246 Preservation and Restoration of Tooth Structure

� Site 2 � approximal enamel in relation toareas in contact with adjacent teeth

� Site 3 � the cervical one third of the crown or,following gingival recession, the exposedroot

However, as caries can be a progressive disease,it is desirable to be able to define the size andextent of the lesion at the time of identificationand, therefore, the potential complexity of therestorative procedures required for treatment. Itis possible then to define five separate sizes as thelesion progresses:

� Size 0 � the earliest lesion that can be identi-fied as the initial stages of demineralisation.This needs to be recorded but will be treatedby eliminating the cause and should there-fore not require further treatment,

� Size 1 � minimal surface cavitation withinvolvement of dentine just beyond treat-ment by remineralisation alone. Some formof restoration is required to restore thesmooth surface and prevent further plaqueaccumulation,

� Size 2 � moderate involvement of dentine.Following cavity preparation remainingenamel is sound, well supported by dentineand not likely to fail under normal occlusalload. The remaining tooth is sufficientlystrong to support the restoration,

� Size 3 � the lesion is enlarged beyond moder-ate. Remaining tooth structure is weakenedto the extent that cusps or incisal edges aresplit, or are likely to fail if left exposed toocclusal load. The cavity needs to be furtherenlarged so that the restoration can bedesigned to provide support to the remain-ing tooth structure,

� Size 4 � extensive caries or bulk loss of toothstructure e.g. loss of a complete cusp orincisal edge, has already occurred.

The Size 0 lesion will be new and may be diffi-cult to identify. The immediate treatment will beto eliminate the disease and thereby bring aboutremineralisation. Size 1 lesions will necessarilyalso be a new lesions and minimal cavity designs,followed by restoration with adhesive materials,will be indicated. Sizes 2, 3 and 4 may mean a newlesion that has progressed to a considerableextent without the patient presenting for treat-ment or it may be replacement dentistry followingbreakdown of an old restoration. The same basicprinciples for developing a cavity design willapply in both cases and, for obvious reasons, thelarger the cavity the greater the problems inrestoration and the shorter the probable longevityof the plastic restorative materials. The selectionof the most suitable material for the largerrestorations will be dictated by such properties asresistance to fracture and flexure as well as abra-sion resistance.

To assist in communication the relationshipbetween Black�s classification and the modernsite and size concept is shown below.

Site 1: Size 0, 1, 2, 3 and 4 - Pit and fissure caries � Cavity located on the occlusal surface of a pos-

terior tooth or any simple enamel defect on anotherwise smooth surface of any tooth.

� Black Class I � the smaller Sizes 0 and 1 couldnot be carried out previously because suitablerestorative materials were not available so theBlack classification begins with Site 1, Size 2(1.2).

TABLE 14.1: Classification of caries lesions

No cavity0

Minimal1

Moderate2

Enlarged3

Extensive4

Pit/fissure1

1.0 1.1 1.2 1.3 1.4

Contact area2

2.0 2.1 2.2 2.3 2.4

Cervical3

3.0 3.1 3.2 3.3 3.4

Table 14.1. A diagrammatic representation of the proposed classification so that the user canvisualise the relationship of the Siteand Size concept for the descriptionof lesions of the crown of a tooth.

SIZESITE

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Classification and Cavity Preparation for Caries Lesions 247

Site 2: Size 0, 1, 2, 3 and 4 � Approximal lesion commencing in relation to contact areas � Cavity located on the approximal surface of

any tooth (anterior or posterior) initiated inrelation to the contact area between two teeth.

� Black Class II � lesions occurring between pos-terior teeth only. Because of difficulties ofidentification and materials limitations therewas no equivalent of Size 0 or 1 so the Blackclassification begins with Site 2, Size 2 (2.2).

� Black Class III � lesions occurring between ante-rior teeth only.

� Black Class IV � an extension of a Class IIIlesion involving the incisal corner or incisaledge of an anterior tooth. An alternative causewould be traumatic fracture of the incisal cor-ner � now classified Site 2, Size 4 (2.4).

Site 3: Size 0,1,2,3 and 4 � Cervical lesions� Lesion located in the cervical region anywhere

around the full circumference of a tooth inc-luding exposed root surface following reces-sion.

� Black Class V � this classification does notrecognise lesions on the gingival third of theapproximal surface, particularly root surface

TABLE 14.2: Comparison

Proposed classification Equivalent Black classification

Site 1 � Pits and fissures andsmooth surfaces

Class I � Pits & fissures

Size 0 � fissure seal Not classified

Size 1 � minimal surgery Not classified

Size 2 � equivalent to BlackClass 1

Class I

Size 3 � requires protection ofremaining tooth structure

Class I

Size 3 � lost cusp or similar Class I

Site 2 � Contact area, allteeth

Class II � contact area,posterior teeth

Size 0 � surface demineralisation

Not classified

Size 1 � beyond remineralisation

Not classified

Size 2 � moderate involvement Class II

Size 3 � requires protection ofremaining tooth structure

Class II

Size 4 � bulk loss of tooth structure

Class II

Class III � contact area,anterior teeth

Not classified

Not classified

Class III

Class III

Class III

Class IV � incisal edgelost, anterior tooth

Not classified

Not classified

Class IV

Class IV

Class IV

Site 3 � cervical third Class V � cervical third

Size 0 � surface demineralisation

Not classified

Size 1 � minimal intervention Not classified

Size 2 � more extensive Class V

Size 3 � approximal root surface

Class II

Size 4 � two or more surfaces Class V

Table 14.2. Demonstrating the difference between the originalG. V. Black classification and the new proposal. The main difference is that the earliest signs of demineralisation can berecorded with this system and the numerical identification fitswell with computerisation of records.

Fig. 14.1. The crown of a bicuspid tooth showing the threeSites where caries is normally initiated: 1. occlusal fissures,2. proximal contact areas, 3. cervical regions around the full circumference of the tooth.

1

23

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248 Preservation and Restoration of Tooth Structure

caries, as being different from Class II les-ions. An erosion/abrasion lesion or a small car-ious cavity on the buccal or lingual surfacewould be a Site 3, Size 0 (3.0) if it was expectedto be arrested. If restoration was required itwould be Site 3, Size 1 (3.1). A larger cariouslesion would be classified as Site 3, Size 2 (3.2).An interproximal lesion would generally beSite 3, Size 3 (3.3) because of difficulty ofaccess. The Site 3, Size 4 (3.4) classification isreserved for a complex lesion involving morethan one tooth surface.

Cavity design and preparationIt will be noted from the above that the Black�sclassification did not allow for the Size 0 or Size 1lesion in either Site 1 or 2 because, in the absenceof radiographs, they could not be identified. Also,in the absence of adhesive restorative materialsthe Size 1 could not be repaired in the proposedminimal manner.

It must be recognised that there is a clear divi-sion between restoring a new lesion and replacinga failed restoration. When dealing with new activecaries the cavity design should be very conserva-tive because it is possible to remineralise bothenamel and dentine which is only partly deminer-alised and not denatured and cavitated. Marginsneed be extended only to smooth surfaces whichare capable of remineralisation and the concept ofremoval of all demineralised tooth structure onthe theory of extension for prevention no longerapplies. Cavity outline form should be dictatedonly by actual cavitation of the surface so thismeans it is often possible to maintain tooth totooth contact interproximally. In fact, with theSize 1 and 2 lesion the prime object of the restora-tion is simply to restore the smooth surface of thecrown to prevent further plaque accumulation.

When dealing with an erosion/abrasion lesion itis essential to diagnose and eliminate the cause toensure longevity for any restorative material cho-sen for repair.

On the other hand, in replacement dentistry, thecavity outline is already defined and will often bemore extensive than ideal. For these restorationsmost of the principles laid down by Black will still

apply, if for no other reason than tooth structurecannot be replaced. In fact, for both Size 3 andSize 4 lesions very little has changed.

Whether the problem presenting is a new lesionor replacement of a failed restoration, the limita-tions of the physical properties of both theremaining tooth structure and the restorativematerial must be taken into consideration. Asmall restoration can be reliably supported byremaining tooth structure, particularly in thepresence of adhesive restorative materials. Infact, it is claimed that a tooth crown can berestored to full physical strength by placing thesematerials. However, as the cavity enlarges thetooth becomes weaker until it reaches a pointwhere the restoration must be designed in such away that the restorative material itself will sup-port remaining tooth structure and protect it fromocclusal load. This requires modification to cavitydesigns and some consideration as to which mate-rial to utilise. These factors are taken into accountwithin the classification.

With the foregoing in mind, treatment of each ofthe lesions mentioned in the classification will bediscussed. However, it must be noted that there isno intention of specifying the actual cavity designor the method of restoration for any lesion. Thesedecisions are left to the operator to decide accord-ing to prevailing conditions for each patient.

SITE 1 LESIONS

Lesions identified under this classification willgenerally commence in fissures on the occlusal

surface of a posterior tooth. Pits on the lingual ofupper anterior teeth are not uncommon and mayalso occur on the buccal surface of lower molarsand the lingual extension of the distal occlusalgroove of upper molars. Erosion and attritionlesions on the occlusal surfaces of posteriors andthe incisal edges of anteriors should also beincluded.� Site 1 � Size 0 (1.0)

No equivalent in the G. V. Black classificationA pit or fissure on any tooth or an erosion

lesion on an incisal edge that is regarded as

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Site 1 Lesion: Classification and Cavity Preparation for Caries Lesions 249

suspicious and in need of observation and pre-ventive measures.

� Site 1 � Size 1 (1.1)No equivalent in the G. V. Black classification

Small defect in one section of a pit or fissureand will often be restored in combination withplacement of a fissure seal on the remainder ofthe fissure system.

� Site 1 � Size 2 (1.2)Moderate size lesion with all fissures involvedor replacement of an existing Black Class Irestoration.

� Site 1 � Size 3 (1.3)A larger lesion requiring incorporation of pro-tection of one or more cusps within the design.

� Site 1 � Size 4 (1.4)Extensive lesion with one or more cuspsalready missing

Site 1 � Size 0, designated 1.0No equivalent in the G. V. Black classificationThe typical lesion is generally represented by anocclusal fissure on a posterior tooth. However,there are similar defects in the enamel that can benoted in areas like the cingulum pits at the lin-gual of upper laterals or the buccal pits on lowermolars. The eroded tips of the cusps of posteriorsor incisal edges of anteriors can also be recorded

in this category. Specifically these lesions do notneed to be restored, simply identified. It is impor-tant to diagnose the cause of the lesion and thecaries risk situation and prevent progress (Chapter6). This is not always simple but will necessarilyrequire investigations in to the caries status of thepatient.

Anatomy of the fissure systemBefore considering the prevention or restorationof a fissure lesion it is necessary to understandthe development and anatomy of fissures.6,7

Diagnosis and treatment of the fissure systems ofthe posterior teeth has always been difficult andcontroversial. It seems that nearly all posteriorshave complex fissures but for a variety of reasonsonly a percentage of them become carious (Figures14.2 and 14.3). Fissures form during calcification ofthe crown of the tooth. Calcification commencesat the tip of the cusps and, as the cusps grow, theywill fuse to some degree at the completion of theocclusal surface of the crown. Fusion will notalways be complete and in a high percentage ofcases there will be defects within the area offusion ranging from single deep pits to extendedgrooves with limited opening to the outer surfacebut relatively large defects in the depths of the fissure. It is virtually impossible to determine the

Fig. 14.2. A photomicrograph using transmitted light showingthe earliest signs of a caries lesion at the base of an occlusal fissure. Note the signs of the development of the translucentdentine below the fissure resulting from the deposition of additional mineral in the lateral tubules as a result of stimulation of the pulp arising from the presence of the caries.

Fig. 14.3. A scanning electron micrograph of the same lesionshown in Figure 14.2. Note the level of development of thelesion in the enamel without overt signs in the dentine.However, the dentine is already involved as demonstrated inthe previous figure.